Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Some radio frequency (“RF”) communication networks make use of omnidirectional antennas due to their simplicity and versatility. But for long distance or high data rate communications, high gain antenna arrays or reflectors may be used. This is particularly true for satellite or unmanned aerial vehicle communications, as well as high data rate millimeter-wave applications. Such antenna arrays generally make use of a technique called beamforming in order to increase gain.
Generally, beamforming is carried out by configuring an antenna array to transmit a focused waveform toward a receiving antenna array, and configuring the receiving antenna array to receive a focused waveform from a particular direction. In one particular example, the transmitting antenna array is configured to vary the phase or amplitude of the signal transmitted by each transmitting antenna of the array in order to generate the focused waveform. Likewise, each antenna of the receiving antenna array is configured to receive a signal of variable phase or amplitude and combine these signals together to reconstruct the focused waveform.
One potential drawback to current beamforming approaches is that the transmitter requires a priori knowledge of the intended target so that the receiver can appropriately point the beam. Likewise, the receiver requires a priori knowledge of the configuration and the transmission direction of the transmitting antenna array in order to successfully receive the focused waveform. If either the transmitter or receiver is moving, then mechanical steering or active electronic steering is typically used to maintain alignment. But these components tend to be bulky and expensive. Additionally, without such a priori knowledge mentioned above, and particularly in situations where the available spectrum is congested, the receiver faces a challenging scenario in attempting to operate in a dynamic, contentious environment with transmitters located at potentially arbitrary or unknown locations and transmitting on potentially arbitrary or unknown frequencies. Yet another drawback exists with current beamforming approaches: they tend to be band-limited. Thus, for systems that communicate across multiple bands, utilizing beamforming approaches dramatically increases costs.